1. Field of the Invention
The present invention relates generally to vibratory material feeders, and in particular to spring systems for vibratory feeder drives.
2. Related Art
Vibratory feeders basically comprise material trays which are connected via spring arrangements to shock-mounted drives or actuators, which impart vibratory movement to the trays via the spring arrangements for movement of material disposed on the trays in a series of jumps or throws. The distance of the throws is a function of the tray displacement magnitude and frequency, and the displacement or throw angle.
In order to be able to use the same actuator with different sized trays having significantly different masses, it is necessary to be able to change the connecting springs. Further, it is desirable to mount the front and rear springs at differing inclinations relative to the path of tray displacement in order to compensate for rotational or rocking motion of the tray and to adjust the "flip ratio", i.e., the ratio of the vertical components of throws at the outlet B and inlet A, respectively, of a tray. (It will be appreciated that for any throw angle a throw will have vertical v and horizontal h components. The vertical component v.sub.B must always be larger than v.sub.A so that the material is accelerated from the inlet to the outlet. The ratio v.sub.B /v.sub.A preferably should be &lt;2, but never 1. As the actuator works to displace the tray in a rearward direction, the rear shock mounts (adjacent the tray inlet A) sag, which causes v.sub.B to increase and v.sub.A to decrease. This can be corrected by enlarging the vertical component of the rear spring.)
In view of the foregoing, spring mounting arrangements have been developed which permit spring replacement and adjustment of the spring inclination. Two examples of such adjustably mounted springs are disclosed in U.S. Pat. Nos. 4,356,911 to Brown and 2,997,158 to Moskowitz et al. In the Brown arrangement, front and rear leaf springs are each clamped to a pair of spaced mounting blocks which are in turn pivotably mounted to vertical support surfaces by screws aligned on a common laterally extending axis. When the block mounting screws are loosened, the blocks may be pivoted about the common axis to adjust the transverse angle inclination of the associated spring relative to a vertical line, and thereby adjust the vertical component of tray displacement. In the Moskowitz et al arrangement, the support springs are mounted on non-parallel planar support faces with removable clamps which are connected to the actuator base through resilient mounts. To adjust the degree of front end flip, Moskowitz proposes either to change the angles of the springs by machining the support faces or changing the effective lengths of the mounting clamp resilient mounts using insertable shims; or to change the stiffness of the springs or the positions of the resilient clamp mounts relative to the center of gravity of the actuator base.
Both of the foregoing spring mounting arrangements have a number of disadvantages. For example, the Brown arrangement is relatively complex and requires precise machining of the screw mounting holes and positioning of the respective support surfaces to ensure that the mounting blocks for each spring have a common pivot axis. In the case of the Moskowitz et al arrangement, only the proposed shims can be used without structurally modifying the remainder of the actuator, and even the shims require substantial disassembly of the actuator.